1. Field of the Invention
This invention relates to moisture separators for use in turbine apparatus and, more particularly, to moisture separators for extracting moisture from the steam/water mixture exiting a high pressure steam turbine to obtain an increased level of steam dryness before it enters a moisture separator reheater.
2. Description of the Prior Art
FIG. 1 illustrates a large steam turbine apparatus 10 such as commonly used in large central station power generation facilities and includes a first, high pressure turbine section 12 and a second, low pressure turbine section 14. A steam/moisture mixture is successively expanded through the high pressure turbine section 12 and the low pressure turbine section 14 to rotate a turbine rotor 15, which is coupled to the rotator of an electrical generator 11. Steam/moisture transmission between the high pressure turbine section 12 and the low pressure turbine section 14 is provided by a crossover structure 20 arranged therebetween. The steam/moisture mixture flows through the turbine apparatus 10, entering an inlet opening 17, expanding through the high pressure turbine section 12 to exhaust portions 16, leaving through exit nozzle or outlet openings 24, passing through one or more moisture separator reheaters 13 (only one illustrated) and the crossover structure 20, entering inlet opening 18 of the low pressure turbine section 14, and expanding through the low pressure turbine section 14.
The crossover structure 20 includes the moisture separator reheater 13, which reduces the moisture content of the steam/moisture mixture exiting the high pressure turbine section 12 to thereby improve turbine efficiency, to reduce the low pressure turbine exhaust moisture, and to reduce maintenance on the low pressure turbine section 14. The moisture separator reheater 13 includes a single pressure vessel and a moisture separator therein for receiving the steam/moisture mixture and for removing and draining moisture therefrom. The steam rises above the moisture separator and passes over two tube bundles 21, where it is reheated by steam from the main steam header and from the high pressure turbine section 12. Typically, the moisture separator may extract approximately 10% of the steam/moisture mixture as moisture, the remaining 90% of the mixture passing to the reheater in the form of the tube bundles 21. The outlet conduit 22 from the moisture separator reheater 13 is provided with two automatic valves 19a and 19b, which close on a turbine trip and control overspeed of the steam turbine 10, which would result from the expansion of entrained steam in the high pressure turbine section 12 and reheaters through the low pressure turbine 14. A hot reheated steam/moisture mixture is conveyed to the low pressure turbine 14. It is understood that more than one low pressure turbine 14 may be included within the steam turbine apparatus 10 depending on the required electrical output.
The outlet conduit 22 is typically identified as being part of the crossover conduit structure 20 disposed between the high and low pressure turbine sections 12 and 14. The steam/moisture mixture passing through such crossover conduit structure 20 has a thermodynamic state, which falls in the so called "wet region" where some moisture has condensed. Such condensation has the propensity for collecting on the inside of the crossover conduit structure 20 and on the outlet opening 24 of the high pressure turbine section 12. Droplets of the collected moisture are intermittently stripped from the interior surface of the crossover conduit structure 20 by the high velocity of steam/moisture mixture passing therethrough. The separated droplets are accelerated by the high velocity mixture, striking many components of the low pressure turbine section 14 and, thus, causing erosion of its turbine rotor and blades. Such erosion can adversely affect the performance and reliability of the low pressure section 14, as well as the crossover conduit structure 20. Further, the conduit leading from the outlet openings 24 to the moisture separator reheater 13 is typically made of carbon steel piping and may be subject to substantial erosion. This conduit, the moisture separator reheater 13 and the outlet conduit 22 had been particularly subject to erosion, where the steam turbine apparatus 10 has significant operating service typically five years or more.
The prior art has many examples of efficient moisture separators, which are modular and could be coupled into the steam turbine apparatus 10, as shown in FIG. 1. In order to connect such moisture separators, a specially designed conduit would be required to interconnect the high pressure turbine 12 and the contemplated modular moisture separator and, in turn, the modular separator and the moisture separator reheater 13. In addition to expense, such interconnected moisture separators would decrease the velocity of the steam passing therethrough and impart an undue pressure drop to the steam as it passes to the low pressure turbine section 14.